The present invention relates to a method for treating tissue. In particular, the present invention relates to a method of controlling thermal therapy of tissue such as the prostate to enhance treatment effectiveness with minimal treatment time.
The prostate gland is a complex, chestnut-shaped organ which encircles the urethra immediately below the bladder. Nearly one third of the prostate tissue anterior to the urethra consists of fibromuscular tissue that is anatomically and functionally related to the urethra and the bladder. The remaining two thirds of the prostate is generally posterior to the urethra and is comprised of glandular tissue. The portion of the urethra extending through the prostate (i.e., the prostatic urethra) includes a proximal segment, which communicates with the bladder, and a distal segment, which extends at an angle relative to the proximal segment by the verumontanum.
Although a relatively small organ, the prostate is the most frequently diseased of all internal organs and is often the site of a common affliction among older men, benign prostatic hyperplasia (BPH), as well as a more serious affliction, cancer. BPH is a nonmalignant, bilateral expansion of prostate tissue occurring mainly in the transition zone of the prostate adjacent to the proximal segment of the prostatic urethra. As this tissue grows in volume, it encroaches on the urethra extending into the region of the bladder neck at the base of the bladder. Left untreated, BPH causes obstruction of the urethra which usually results in increased urinary frequency, urgency, incontinence, nocturia and slow or interrupted urinary stream. BPH may also result in more severe complications, such as urinary tract infection, acute urinary retention, hydronephrosis and uraemia.
Benign prostatic hyperplasia (BPH) may be treated using transurethral thermal therapy as described in further detail in U.S. Pat. No. 5,620,480 entitled METHOD FOR TREATING BENIGN PROSTATIC HYPERPLASIA WITH THERMAL THERAPY and in U.S. Pat. No. 5,575,811 entitled BENIGN PROSTATIC HYPERPLASIA TREATMENT CATHETER WITH URETHRAL COOLING, both of which are hereby incorporated by reference. During transurethral thermal therapy, the transition zone of the prostate is heated to necrose the tumorous tissue that encroaches on the urethra. Transurethral thermal therapy is administered by use of a microwave antenna-containing catheter which includes a multi-lumen shaft. The catheter is positioned in the urethra with the microwave antenna located adjacent to the hyperplastic prostatic tissue. Energization of the microwave antenna causes the antenna to emit electromagnetic energy which heats tissue within the prostate. A cooling fluid is circulated through the catheter to preserve tissue such as the urethral wall between the microwave antenna and the target tissue of the prostate.
The primary goal of transurethral thermal therapy is to necrose prostate tissue while preserving adjacent healthy tissue. It is also preferable to achieve this goal in as short of a time as is possible, consistent with the patient's level of tolerance and comfort. In addition, it is important that the rectum be preserved from unduly high temperatures, since it is susceptible to thermal damage. There is an ongoing need in the art for a method of controlling thermal therapy that reduces treatment time and enhances effectiveness consistent with all of these parameters.